Magistrate Liu was taken down because Qin Liuxi sent over a series of evidence of his corruption and exploitation of the people. The Inspector's rapid arrival was due to his acquaintance with Qin Liuxi, Governor Xiao.
Governor Xiao was rigid but loyal and straightforward, albeit not very tactful, leading him to remain in the same position for several years. He had a chance for promotion last year but managed to offend his superiors and was subsequently passed over.
He didn't mind himself much; after all, as the saying goes, ten years as a Magistrate. He's only been the Governor of Ningzhou for eight years and can wait. Aren't there County Magistrates who are reappointed after three years?
